2-O-Methylhonokiol Suppresses 3T3-L1 Adipogenesis Through Metabolic Stress Signaling and Early Cell Cycle Restriction

Excessive adipose tissue expansion contributes to metabolic dysfunction, highlighting the need to identify compounds that restrain adipocyte differentiation without causing nonspecific cytotoxicity. This study investigated whether 2-O-methylhonokiol suppresses adipogenesis in 3T3-L1 preadipocytes and examined its effects on adipogenic transcription, metabolic signaling, ER stress-related responses, kinase activity, and early cell cycle progression. 3T3-L1 cells were induced to differentiate with an MDI cocktail and treated with 25 or 50 µM 2-O-methylhonokiol during differentiation. Lipid accumulation was evaluated by Oil Red O staining, protein expression and phosphorylation were analyzed by immunoblotting, cell cycle distribution was assessed 24 h after MDI induction, and basal viability was measured using the CCK-8 assay. 2-O-methylhonokiol markedly reduced neutral lipid accumulation and suppressed key adipogenic regulators and maturation markers, including C/EBPβ, PPARγ, C/EBPα, FABP4, and FASN. At the signaling level, 2-O-methylhonokiol increased AMPKα phosphorylation without altering total AMPKα and reduced FASN expression, whereas mTOR phosphorylation was reduced at 50 µM. These findings suggest that 2-O-methylhonokiol is associated with metabolic and lipogenic signaling remodeling during adipocyte differentiation. 2-O-methylhonokiol also modified kinase-associated responses, increasing AKT and JNK phosphorylation while reducing the detectable phosphorylated ERK signal, with total AKT, ERK, and JNK remaining largely unchanged. ER stress-related signaling displayed a selective profile, characterized by increased IRE1α expression, XBP1s induction, elevated p-eIF2α, unchanged total eIF2α, and no compensatory increase in GRP78. During early adipogenesis, 2-O-methylhonokiol attenuated MDI-induced cell cycle redistribution by preserving a larger G0/G1 population and limiting progression toward later cell cycle phases, consistent with impaired mitotic clonal expansion. These effects occurred at concentrations that did not significantly reduce basal cell viability. Overall, 2-O-methylhonokiol suppresses 3T3-L1 adipogenesis by reducing adipogenic and lipogenic execution, accompanied by AMPK-associated metabolic remodeling, kinase signaling changes, selective ER stress-related responses, and restriction of early cell cycle progression. Further pathway-specific studies are required to define the causal contribution of each signaling axis.